Friday, April 28, 2017

Fixing and Fettling a Wooden Plow / Plough Plane - Part 4

Parts 1, 2 and 3 of this series of posts are here, here and here.  When I left off, I had sent the crappy set of irons back to the seller and I was looking for a decent set.  Ideally it would be a set from Ohio Tool Co. to match the plane.  But I was told that they can be tough to find (and big bucks) and that British sets can be found more easily (and inexpensively).  I ended up getting a set of Thomas Ibbotson irons #1 through #8 that were in pretty decent shape.
Same emblem on all 8 irons
Thomas Ibbotson & Co. were in business from about 1830 to 1905, when Marples bought them.
Don't let the rust fool you - they're in good shape
After the usual citric acid treatment (except this time I left them overnight) and a little sanding, they looked a lot better.
A nice difference
And here's the beveled / grooved side
Almost immediately, a fine layer of rust appeared, especially on the sides.
Looked like this within a few minutes of being perfectly rust-free
So I re-sanded and immediately wiped down the irons with a cloth dampened with 3-in-1 oil.

These irons are interesting.  Each iron is laminated from two pieces of metal, and the part that takes an edge does not go all the way from sharp end to back end.  You can see the junction in the following picture (bevel side is down).
You can see where the lamination begins
All the bevels were ground at something close to 25°, so I only really needed to clean up the bevel and then grind a secondary bevel at 30°.  These came out pretty nice, though the pictures make it look like I didn't grind them square to a side.
Sizes #8 to #3
Here's an interesting thing - I thought the sizes would be closer to the expected 1/8" to 5/8" than they are.  Here are the nominal and actual sizes:

  • Number     Nominal     Decimal Nominal     Actual Size (diff. from nominal)
  • #1              1/8"            0.125"                       0.152" (+0.027",not all that close!)
  • #2              3/16"          0.187"                       0.199" (+0.012")
  • #3              1/4"            0.250"                       0.263" (+0.013")
  • #4              5/16"          0.312"                       0.324" (+0.012")
  • #5              3/8"            0.375"                       0.386" (+0.011")
  • #6              7/16"          0.437"                       0.418" (- 0.019")
  • #7              1/2"            0.500"                       0.495" (- 0.005"
  • #8              5/8"            0.625"                       0.561" (- 0.064" (more than a 16th undersized!)
Maybe the #8 is really 9/16" nominal.  Either way, one thing I've learned from hand tool woodworking: the actual sizes are not that important - you make parts to fit to grooves you plow.

With the irons sharp, I couldn't wait to make a test cut.  The original wedge didn't fit well with the 1/8" iron (or any of the others), so the planing was not as smooth as it could have been, though it still worked.
First test cut in oak with #1 iron
The next and last post of this series will be about making and fitting new wedges and a few test cuts.


  1. Where did you take the measurements Matt? Ibbotson had a good reputation and I'm surprised these are so far off.
    I just measured my mixed english set of plow plane irons and they are all are over the nominal. It shouldn't make any difference as long as you reference everything off of them. But still, I would have expected a tighter tolerance. 1-8 .166 .198 .261 .325 .400 .448 .523 .571 I measured all of mine at the end of the iron.

    1. Ralph, I made sure to measure at the business end, side to side. Had to register off the edges because the iron tapers down on the bevel side. Just for kicks, I checked to see if my decimal measurements were close to any whole number metric values, but no go there, too. Your numbers are pretty far off, too. I guess we both have to make sure to keep that in mind when it comes time to use it.

  2. Yeah, and none of my plow irons agrees with any of my mortice chisels, which aren't particularly close to nominal either! Oh well, a mortice doesn't really need to be as wide as the groove next to it.

    1. Hi Kees. Sure would be nice if these things were standardized. But I've got to realize that a hundred years ago things were bound to be different.

  3. Nice set of plow irons.
    As you found out, it is very usual to find under or over sized tooling with antique tools. Sizes are nominal, were hand forged and due to rust and subsequent cleaning, sharpening etc get a smidge smaller. Mixing tooling between makers, country of origins or even vintage period also will results in inconsistency. You will rarely if ever find actual bang on measurements on antique. Do we care? Not really, you use the tools to make its corresponding groove and match it with a similar sized chisel. As Kees found out, no guarantees of this happening neither with various tooling...
    The only thing that really matter are the fact that you got a nice graduated set (No 1 to 8)

    Exact measurements is really a more modern invention

    Bob, the old tool guy

  4. That looks like great set of laminated irons. I'm not too surprised by the variances in the sizes. Keep in mind that bolts and nuts were not globally standardized until 1948. As Bob stated, "Exact measurements is really a more modern invention".

    1. Yes, I'm finding this out. I guess this is all part of the transition from power tool thinking/woodworking to hand tool thinking/woodworking.

  5. I think I have the same plane.

    Two comments on the sizing discrepancy.

    One is that the groove closes in slightly on the cutter if you aren't tilting the plane in use. The sides of the grooves are a little ragged and won't match the dimension of the cutter exactly.

    Second, the sides of the cutters are relieved so they don't bind in the groove when it is slightly smaller above the edge. Gradually, the cutter will narrow over its life but that is decades of use for a hobbyist. Trying to narrow the cutter by grinding down will have to replicate this side relief or the cutter will lock up badly in deep cuts.

    For the cutters that are .010 over, I would recommend cutting a groove and then put a strip of wood the nominal thickness in to check the fit. It may not be as loose as you are expecting.

    Good luck.

    1. Thanks for the comments, Steve. I had noticed that the irons are narrower on the bevel side than on the flat side and realized that this was for clearance. I did have a passing thought about grinding the irons to the nominal thicknesses, but I wasn't actually going to attempt it.